自己动手写一个简单的ping命令（windows下）

计算机网络的一个作业：实现ping+ip 不要求其它参数

用到的知识：ip报头结构，icmp报头结构，获取主机ip方法，winsock的简单操作

实现的结果：一般的ip能够ping通，如www.baidu.com, www.sina.com.cn

存在的问题：本机（127.0.0.1）ping不通  

/*
*filename:ping.c
*author:ChrisZZ
*/
#pragma comment(lib, "ws2_32.lib")
#include <stdio.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <process.h>


struct IPHeader{//IPv4头部结构
    unsigned char ver_hlen;//头部长度，用4位表示，range[5,15]
    //  unsigned int ver:4;//version
    unsigned char tos;//type of service
    unsigned short total_len;
    unsigned short id;
    unsigned short frags_and_flags;
    unsigned char ttl;//time to live
    unsigned char proto;//protocal
    unsigned short chksum;//checksum
    unsigned int srcIp;//source IP
    unsigned int dstIp;//destination IP
};

struct ICMPHeader{//ICMP头部结构
    unsigned char type;
    unsigned char code;
    unsigned short chksum;
    unsigned short id;
    unsigned short seq;//sequence
    unsigned int timestamp;
};

#define ICMP_ECHO       8
#define ICMP_ECHO_REPLY 0
#define  PACKAGE_SIZE         sizeof(IPHeader)+sizeof(ICMPHeader)
void usage();
unsigned short CheckSum(unsigned short*, int);
void HandleError(char *);

//用法说明函数
void usage(){
    printf("用法：ping 目标主机\n\n");
    system("pause");
}

//错误处理函数
void HandleError(char *str){
    int errCode=WSAGetLastError();

    char info[65]={0};
    _snprintf(info, 64, "%s:  %d\n", str, errCode);
    printf(info);
}

unsigned short checksum(unsigned short* buff, int size){
    unsigned int chksum=0;
    while(size>1){
        chksum+=*buff++;
        size-=sizeof(unsigned short);
    }
    if(size){
        chksum+=*(unsigned char*)(buff);
    }
    chksum=(chksum>>16)+(chksum &0xffff);
    chksum+=(chksum>>16);
    return (unsigned short)(~chksum);
}

void FillPackage(char *pData, unsigned int dstIP, unsigned short id){
    memset(pData, 0, PACKAGE_SIZE);

    IPHeader *pIPHeader=(IPHeader*)pData;

    int nVersion=4;
    int nHeadSize=sizeof(IPHeader)/4;

    //获得本机IP
    struct sockaddr_in SrcAddr;
    struct hostent * hpsrc;
    char localhost[32];
    gethostname(localhost, sizeof(localhost));
    hpsrc=gethostbyname(localhost);
    memset(&SrcAddr, 0, sizeof(SrcAddr));
    memcpy(&(SrcAddr.sin_addr), hpsrc->h_addr, hpsrc->h_length);
    SrcAddr.sin_port=htons(0);
    SrcAddr.sin_family=AF_INET;


    unsigned int srcIP=SrcAddr.sin_addr.s_addr;//本机IP
    unsigned int destIp=dstIP;
    pIPHeader->ver_hlen=(nVersion<<4)|nHeadSize;
    pIPHeader->tos=0;
    pIPHeader->total_len=htons(PACKAGE_SIZE);
    pIPHeader->id=htons(1234);//????
    pIPHeader->frags_and_flags=0;
    pIPHeader->ttl=255;//??
    pIPHeader->proto=IPPROTO_ICMP;
    pIPHeader->chksum=0;
    pIPHeader->srcIp=srcIP;
    pIPHeader->dstIp=dstIP;

    pIPHeader->chksum=checksum((unsigned short*)pData, sizeof(IPHeader));
    ICMPHeader* pICMPHeader=(ICMPHeader*)(pData+sizeof(IPHeader));
    pICMPHeader->type=ICMP_ECHO;
    pICMPHeader->code=0;
    pICMPHeader->chksum=0;
    pICMPHeader->id=htons(id);
    pICMPHeader->seq=htons(id);
    pICMPHeader->chksum=checksum((unsigned short*)((char*)pData+sizeof(IPHeader)), sizeof(ICMPHeader));

}

int main(int argc, char* argv[]){

    //初始化
    WSADATA wsaData;
    struct sockaddr_in DestAddr,from;
    IPHeader *ip;
    ICMPHeader *icmp;
    ICMPHeader *SendIcmp;
    int Timeout=1000;
    char IcmpBuffer[PACKAGE_SIZE]="";
    SOCKET IcmpSocket;
    char RecvBuffer[1024];
    sockaddr_in addr;
    int Len = sizeof(addr);
    int Result;
    struct hostent * hpdst;
    int pid=_getpid();
    struct timeval tv;
    fd_set readSet;
    BOOL bBroadcast=false;

    //确定参数个数
    if(argc!=2){
        printf("参数不正确\n");
        usage();
        return -1;
    }


    if ((Result = WSAStartup(MAKEWORD(2, 2), &wsaData)) != 0){
        printf("WSAStartup failed with error %d\n", Result);
        return 0;
    }


    //获取目的主机IP
    hpdst=gethostbyname(argv[1]);
    if(hpdst==NULL){
        HandleError("gethostbyname");
        WSACleanup();
        return -1;
    }

    //创建ICMP封包并发送
    //char buff[sizeof(ICMP_HDR)+32];
    IcmpSocket=socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if(IcmpSocket==INVALID_SOCKET){
        HandleError("socket");
        WSACleanup();
        return -1;
    }
    BOOL on=TRUE;
    Result=setsockopt(IcmpSocket,IPPROTO_IP,IP_HDRINCL, (char*)&on, sizeof(on));
    if(Result==SOCKET_ERROR){
        HandleError("socketopt");
        WSACleanup();
        return -1;  
    }   
    memset(&DestAddr, 0, sizeof(DestAddr));
    memcpy(&(DestAddr.sin_addr), hpdst->h_addr, hpdst->h_length);
    DestAddr.sin_port=htons(0);
    /*reference:http://www.cnblogs.com/CBDoctor/archive/2012/10/28/2743109.html*/
    DestAddr.sin_family=AF_INET;



    int i;
    for(i=0; i<3; i++){
       if(i==0) printf("正在Ping %s 具有 %d 字节的数据:\n", inet_ntoa(DestAddr.sin_addr), 32);

        FillPackage(IcmpBuffer, DestAddr.sin_addr.s_addr/*dstIp*/, (unsigned short)pid);

        Result=sendto(IcmpSocket, IcmpBuffer, PACKAGE_SIZE, 0, (struct sockaddr*)&DestAddr, sizeof(DestAddr));
        if(Result==SOCKET_ERROR){
            HandleError("sendto");
            break;
        }

        while (1){
            tv.tv_sec=3;
            tv.tv_usec=0;
            FD_ZERO(&readSet);
            FD_SET(IcmpSocket,&readSet);

            int res=select(IcmpSocket+1,&readSet,NULL,NULL,&tv);
            if(res==SOCKET_ERROR){
                HandleError("select");
                break;
            }
            if(res==0){
                if(!bBroadcast)
                    printf("请求超时。\n");
                break;
            }
            if(FD_ISSET(IcmpSocket, &readSet)){
                memset(IcmpBuffer,0, PACKAGE_SIZE);
                memset(&from,0,sizeof(from));
                int len=sizeof(from);
                if(recvfrom(IcmpSocket, IcmpBuffer, PACKAGE_SIZE,0,(struct sockaddr*) &from, &len)==SOCKET_ERROR)
                {
                    HandleError("recvfrom");
                    break;
                }

                IPHeader *pIPHdr=(IPHeader *) IcmpBuffer;
                ICMPHeader *pICMPHdr=(ICMPHeader*)(IcmpBuffer+sizeof(IPHeader));
                int nTime = GetTickCount() - pICMPHdr->timestamp;  
                if(pICMPHdr->id==htons((u_short) pid)&&pICMPHdr->seq==htons((u_short) pid)
                    &&pICMPHdr->type==ICMP_ECHO_REPLY){
                        printf("来自 %s 的回复: 字节=%d time=%dms\n",inet_ntoa(from.sin_addr), Result, pIPHdr->ttl);
                        if (!bBroadcast) break;
                } 
            }
        }//end of while
        Sleep(1000);
    }

    //关闭套接字
    closesocket(IcmpSocket);
    WSACleanup();
    system("pause");
    return 0;
}